No. 377-.| AMIOID AND LEPISOSTEOID FISHES. 347 
feebly ossified. Among the Macrosemiidz, as we are informed, 
Ophiopsis possessed ‘completed annular pleurocentra and hypo- 
centra, alternating in the caudal region.” These are doubtless 
true pleurocentra. Mr. Woodward has presented a figure of 
a portion of the vertebral column of Notagogus.! This closely 
resembles that of the young Amia, as shown by my own figures 
(Figs. 1-4). Histionotus is not represented as possessing 
distinct pleurocentra and hypocentra; but the figure in Dr. 
Zittel’s Handbuch (vol. iii, Fig. 231) shows each of the verte- 
bral rings as having an oblique position, as though alternating 
component elements had united. Compare this figure with that 
of Callopterus, Handbuch, p. 231, Fig. 243. 
In the Pachycormide the vertebral elements are feebly 
developed; at most, feebly ossified. Nevertheless, they are 
present in Euthynotus. If we may rely on Dr. Zittel’s figure 
of the vertebral column of this genus, the arch-bearing rings 
were nearly complete; but there were small pleurocentra 
wedged in between them. 
Taking all things together, we cannot doubt that the verte- 
bral axis of the Amiidz, the Eugnathide, the Macrosemiide, 
and the Pachycormidz conforms to the same plan of devel- 
opment, and that this is quite different from that of the 
Lepisosteoid series. 
When we come to examine the vertebral structures of the 
Semionotidz and of the Pycnodontide, we find a very different 
condition. In many genera, indeed, the vertebral elements are 
as feebly developed as in some of the Eugnathide. In Lepi- 
dotus, however, vertebral rings are present; but there are no 
evidences of the presence of two rings for each muscle segment 
in any part of the vertebral column. Mr. Woodward states 
that the rings of Lepidotus seem to consist each of four 
sectors, each of which bears an arcuale. That is, they are just 
such rings as those which bear the arches in the tail of Amia 
(Fig. 2) and such as occur in Lepisosteus. We find no proofs 
in any member of the family that the intercalated cartilages 
were ossified, or that they manifested any tendency to assume 
special importance. 
1 Catalogue, vol. iii, pl. iii, Fig. 10. 
